1. Field of the Invention
The invention relates to a communication device, a multi-band receiver, and a receiver.
2. Description of the Related Art
In order to reduce DC (direct current) offset in an AGC (Automatic Gain Control) circuit equipped in a CDMA (Code Division Multiple Access) receiver, for instance, Japanese Patent Application Publication No. 2003-224488 (patent reference 1) has suggested detecting a period of time in which DC offset in an internal circuit equipped in a direct-conversion type receiver may increase beyond a threshold due to AGC operation, and setting a cut-off frequency of a high pass filter equipped in a base-band variable gain-amplifying circuit, to be higher than a normal frequency in the detected period of time to thereby swiftly converge transient response of signals having passed the high pass filter.
Recently, a user equipment (UE) such as a mobile phone covering a plurality of frequency bands different from one another (for instance, 2 GHz band and 800 MHz band) is being developed.
When inter-frequency handover is to be carried out between different carrier frequencies, it is necessary for a user equipment (UE) to establish synchronization after switching a frequency to another. To this end, a user equipment (UE) is designed to carry out predetermined measurement relating to a carrier frequency which the user equipment would have after handover was carried out, during a period (called “transmission gap”) of time in which a part of frame of active link is ceased to be transmitted, and transfer data included in deleted period of time (that is, data in transmission gap) at a high rate during active period of time, to thereby raise transmission power. Thus, it is possible to maintain a transmission rate and channel quality. Such a control as mentioned above is called “compressed mode” (3GPP Compressed Mode) (for instance, see the non-patent references 1, 2 and 3).
When handover is necessary to be carried out, a base station (BTS) instructs a user equipment (UE) to operate in a compressed mode. A compressed mode is carried out by reducing a dispersion rate, and by deleting bits out of data (that is, puncturing, but only for downlink).
A compressed frame is defined periodically or on request. A compressed frame has variable rate and type, both of which are dependent on environment and requirement for measurement.
As a structure similar to a part of a later mentioned second embodiment in accordance with the present invention, Japanese Patent Application Publication No. 04-297182 (patent reference 2) has suggested an image reader in which two image signals transmitted from CCD (Charge Coupled Device) are amplified in AC amplifiers electrically connected to each other in AC manner through capacitors C1 and C2. Capacitors C3 and C4 are electrically connected at one of their ends to output ports of the AC amplifiers, and at the other ends to DC buffers. The capacitors C3 and C4 are electrically connected at the other ends thereof to each other in accordance with clamp signals.    Patent Reference 1: Japanese Patent Application Publication No. 2003-224488    Patent Reference 2: Japanese Patent Application Publication No. 04-297182    Non-patent Reference 1: 3GPP TS 25.215 V3.10.0 Technical Specification Group Radio Access Network; Physical layer—Measurements (FDD) (Release 1999)    Non-patent Reference 2: 3GPP TS 25.212 V3.11.0 Technical Specification Group Radio Access Network; Multiplexing and Channel Coding (FDD) (Release 1999)    Non-patent Reference 3: 3GPP TS 25.101 V3.17.0 Technical Specification Group Radio Access Network; User Equipment (UE) radio transmission and reception (FDD) (Release 1999)